$\Bbb Z^\ast$ What is this notation?

Question

What does $\Bbb Z^\ast$ mean? I would think some subset of the integers but I cannot find a definition. Thank you.

Answer 1

@dwalke: This means all integers except for 0.

Edit: I'm all the more convinced now that you said it's a "vestibular"-type question. This notation is taught in the standard high-school curriculum in Brazil. See http://www.infoescola.com/matematica/numeros-inteiros/ for example.

Answer 2

I see there is some disagreement, but the notation $R^\ast$ or $R^\times$ with $R$ a commutative ring means the group of units of $R$ to me. With this interpretation, we have $\Bbb Z^\ast = \{\pm1\}$.